Vijay Patel, 49, was attacked in Mill Hill area of the city on Saturday night and rushed to hospital, where he died of head injuries on Monday.

Patel's death bed photograph, hooked up to a life-support machine, has been released by his family as part of an appeal to hunt for suspects involved in the attack.

A 16-year-old boy appeared in court today and was charged with murdering Patel, the father of two.

"The Homicide and Major Crime Command continue to investigate and appeal for information about the events leading up to the incident which resulted in Patel's death. It is believed that three persons were involved in the incident," Scotland Yard said in a statement.

Detective Inspector Ian Lott, from the Metropolitan Police Homicide and Major Crime Command,described the attack as an "unprovoked spontaneous incident sparked entirely by refusal to let the suspects buy what they wanted".

"A man has lost his life for no reason other than trying to uphold the law," he said.

Patel was struck in the chest and fell backwards, hitting his head as he landed.

He was found lying injured on the pavement outside his local convenience store named Rota Express by London Ambulance Service, who rushed him to St. Mary's Hospital in London.

Patel had moved to London with his family from India in 2006 and his wife, Vibha, was visiting relatives in India at the time of the fatal attack.

"We are shocked and heartbroken. He was such a kind person. We are all very close because his children are out of the country studying,"said the victim's brother, Prakash.

The shopkeeper's friends described him as "honest" and "hard-working".